Monocular visionis vision with one eye. If a person is deprived of binocu-
lar vision, then he or she can still perceive depth with the assistance of monocular
cues. (Although the loss of the use of an eye impairsdepth perception, it does not
destroy it completely.) Monocular cuesare available to one eye. These are the
kinds of cues that give a landscape painting depth. Although you normally look at
such a painting with both eyes open, in this case depth perception is not arising
because of retinal disparity. Close one eye and look at the painting. The percep-
tion of depth will remain.
A first monocular cue is linear perspective,the tendency of parallel lines to
seem to converge as they approach the horizon. Linear perspective was referred to
earlier in connection with the Moon illusion. A second monocular cue is inter-
position,a cue created when one object blocks some portion of another object.
If a person is standing in front of a tree, and the tree is partly blocked, it is easy to
see that the tree is behind, not in front of, the person.
A third monocular cue is shadows.Shadows are differences in illumination
gradients. These tend to help us see rounded surfaces as convex or concave. A
fourth monocular cue is texture gradient.A texture gradient is perceived when
we can see less detail in far away objects than those that are closer to us. Such a
gradient appears spontaneously when we look at a field strewn with rocks.
A fifth monocular cue is motion parallax,the tendency when moving for-
ward fairly rapidly to perceive differential speeds in objects that are passing by and
in those that are being approached. For example, in a traveling car, nearby tele-
phone poles approach rapidly and then flash by. Look down the road. The tele-
phone poles seem to be approaching slowly. If you can see telephone poles very
far away, they seem to be almost stationary.
All of these monocular cues work together to enhance depth perception.(a) Monocular vision is vision with.(b) The tendency of parallel lines to seem to converge as they approach the horizon is
called.
(c) Differential speeds are associated with what monocular cue?Answers: (a) one eye; (b) linear perspective; (c) Motion parallax.Extrasensory Perception: Is It Real?
The novel Slanby A. E. van Vogt has become a science-fiction classic. First serialized
in the magazine Astounding Science Fictionin 1940, the story relates the adventures of
a boy with telepathic powers and his conflicts with nontelepathic adversaries. Telepa-
thy has become a staple of science fiction and is taken for granted as a power of the
mind in many novels and films. But is it real?66 PSYCHOLOGY